The need to heat structures to control the interior temperature has been a requirement for modern housing for a long time. One of the current popular methods used to heat structures is with a furnace that burns either oil or natural gas. Due to the increasing costs of fossil fuels, the operating efficiency of furnaces has become a greater and greater concern.
One common method of increasing the fuel efficiency of the burner within a furnace has been to utilize a blower to induce a draft through the furnace to draw the heated air and the products of combustion through a heat exchanger and finally exhaust them through an exhaust pipe. The blower increases the draft such that the heated air and the products of combustion can travel through as tortured a path as possible to increase the amount of heat removed from exhaust gases within the heat exchanger. The increase in the flow of air thereby increases the heat transfer and generating capacity of the burner while simultaneously using less fuel per BTU of heat generated. The addition of a blower motor to a furnace generates a rating of at least 80 percent fuel efficiency in a modern furnace. Thus, it is clearly a necessity to introduce a blower to a modern furnace to maintain minimum desired efficiency standards.
When designing a blower assembly, an important design characteristic is that the blower motor and impeller, as well as the inlet opening and outlet opening, be properly sized such that the blower is able to draw the desired amount of exhaust gases from a furnace to which it is mounted. If the blower motor is underrated, the blower will be under-drawing the flue gases such that the gases leaving the furnace will have a higher than desired concentration of carbon monoxide. Likewise, if the blower motor is oversized, the blower will overdraw the flue gases from the furnace. The overdrawing of the furnace results in an increased volume of the flue gases moving to quickly past the heat exchanger of the furnace, resulting in excessive exhaust temperatures entering into the blower. Thus, the blower assembly, including the blower motor and the impeller, must be properly sized to operate within specified flow characteristics.
A secondary requirement for blower assemblies is that the blower must adequately operate the gas appliance when the voltage used to operate the blower assembly is reduced. Such a reduction in voltage can occur during low power situations, such as a brownout, in the geographic area where the blower is installed.
Presently, multiple solutions have been designed to address the issues identified above. The first solution is to provide a flow restriction at the blower inlet. A flow restriction at the blower inlet accomplishes the need for the gas appliance to operate at a reduced voltage. However, during normal operating conditions, the pressure in the blower housing is reduced, which naturally reduces the efficiency of the blower and requires a larger motor that operates at a higher speed.
A second solution is to restrict the blower outlet with a simple restrictor plate having an orifice. The orifice decreases the efficiency of the blower by reducing the effective diameter of the exhaust outlet. Since the restrictor plate typically extends perpendicular to the flow of exhaust gases, the exhaust gases strike the portions of the restrictor plate surrounding the orifice, which dramatically affects the flow rate out of the blower. Further, a hard restrictor plate at the outlet is very inefficient such that the low voltage requirements for the gas appliance cannot be met. Finally, the hard restrictor plate perpendicular to the direction of exhaust gas flow creates pressure in the exhaust adapter, which requires the joints of the exhaust adapter to be sealed by more effective and expensive means.
Therefore, it is an object of the present invention to provide a blower assembly that allows the blower to perform to properly draw combustion products through a gas appliance while also being operable in a reduced voltage environment to provide acceptable operating characteristics. Further, it is an object of the present invention to provide a blower assembly having a flow restrictor that does not reduce the pressure in the blower housing yet provides for low voltage operation.